The present invention relates to a heat exchanger, and more particularly to a duplex heat exchanger comprising a plurality of unit heat exchangers and adapted for use as the condensers or evaporators in car coolers or room coolers, or for use as the oil coolers for automobiles or the like.
The so-called multi-flow type heat exchanger has attracted public attention in the users mentioned above. This heat exchanger has a structure disclosed for example in the U.S. Pat. No. 4,825,941, such that a plurality of parallel flat tubes are connected to a pair of hollow headers at their opposite ends, respectively, with a corrugated fin interposed between one such flat tube and the next. In operation, heat exchange occurs between a coolant which flows through a coolant circuit composed of said flat tubes and air flows between the tubes. The known multi-flow type heat exchanger can be made thinner than the other known heat exchangers in its dimension in a direction of air flow, without affecting the efficiency of heat exchange. Therefore, said multi-flow type heat exchangers have proved better than the other known heat exchangers of some types such as the serpentine type.
In a case where a higher capacity of heat exchange is needed for the multi-flow type heat exchanger, vertical and/or horizontal dimensions thereof may be restricted by a given space for installation of said heat exchanger. In detail, length and the number of the tubes are generally delimited by the spatial condition. It may thus be regarded as feasible that the width of said tubes, i.e., the depth of said heat exchanger, be increased to meet the required greater capacity.
However, with a width of the heat exchanger as a whole being left unchanged, a larger width of the tubes will inevitably cause an outer diameter of the headers to be increased resulting in decrease of the tube's length effective to heat transfer. This problem has been a bottleneck in increasing the heat transfer capacity to a satisfactory degree.
Fleisher proposed in the U.S. Pat. No. 2,124,291 issued to him on Jul. 19, 1938 a duplex heat exchanger of the type comprising two unit heat exchangers, which were disposed in parallel with each other and fore and aft in the direction of air flow. It may be regarded as possible to simply arrange also fore and aft in the air flow direction the unit heat exchangers which are relatively thin and of the multi-flow type.
Since the headers in each unit heat exchanger constituting the duplex one is generally of a diameter larger than width of its tubes, the tubes in a front unit heat exchanger will be spaced a considerable distance from those in a rear one. Consequently, heat exchange capacity can not necessarily be raised in proportion to the increased depth of the duplex heat exchanger as a whole.
Further, a leeward unit heat exchanger is exposed to an air flow which has already passed through and heated by a windward one in the duplex heat exchanger. An efficient heat exchange cannot be expected between such a warm air and a coolant flowing through the leeward unit heat exchanger. It is also difficult from this point of view to raise heat exchange capacity in proportion to the increased depth of the duplex heat exchanger.
It will be another problem that in a case wherein the prior art duplex heat exchanger is used as an evaporator its leeward unit heat exchanger will scatter an amount of water condensed thereon.